In spline couplings and other such rotary couplings (e.g., epicycle gear couplings), a drive shaft may be received within a cavity provided through annular plate or spine. In certain systems, the spline may translate with respect to the drive shaft. For example, in a ball ramp torque limiter, the spline may comprise a translating plate having a plurality of inner teeth that engage outer teeth provided about the drive shaft. The spline is spring biased toward a second, non-translating plate that is coupled to an output shaft. When the torque at the drive shaft is below a predetermined threshold, the spline and the non-translating plate abutting engage. The spline and the non-translating plate each include a series of conical pockets therein. Each conical pocket provided on the spline cooperates with a pocket on the non-translating plate to form a ramped cavity. An axial load ball bearing resides in each ramped cavity, and generally serves to transfer torque from the spline to the non-translating plate. As the torque limiter rotates, a shear force is exerted on the ball bearings. When the torque at the drive shaft exceeds the predetermined torque threshold (the activation torque), the shear force exerted on the ball bearings exceeds the spring force exerted on the spline. As a result, the ball bearings roll up the cavities' ramped sides and leave their respective cavities. This causes the spline and the non-translating plate to separate thereby permitting the drive shaft to rotate independently of the output shaft. The transfer of torque to the output shaft is thus limited when the torque at the drive shaft exceeds the predetermined threshold.
Rotary couplings typically require lubrication to ensure optimal functioning. In the case of a spline coupling utilized in a ball ramp torque limiter, a lack of lubrication may lead to excessive friction and a consequent increase in the activation torque (i.e., the predetermined torque threshold at which the transfer of torque is interrupted). This increase in the activation torque may, in turn, result in damage to system components. Even after initial application, re-application of lubricant is often required as the lubricant may be expelled at high rotational frequencies by centrifugal forces. If grease is used as the lubricant, the centrifugal force may separate the base oil from the thickener of the grease. Accessing the rotary coupling typically involves a cumbersome process thereby making repeated manual applications of lubrication impractical. Consequently, various sub-systems have been developed that actively supply lubricant to rotary couplings; however, such sub-systems may be relatively complex and expensive to employ. In addition, such sub-systems add to the weight of the rotary coupling, which may be problematic if the rotary coupling is utilized in a system deployed on an aircraft (e.g., a torque limiter employed in a ballscrew actuator). Furthermore, active supply sub-systems may have difficulty conducting thicker lubricants (e.g., grease).
Considering the above, it should be appreciated that it would be desirable to provide a rotary coupling employing a spline having one or more features that facilitate the retention of lubricant. It should also be appreciated that it would be advantageous if such lubricant retaining features also promoted the uniform dispersal of lubricant. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.